From: Yu Kuai yukuai3@huawei.com
[ Upstream commit 4f1731df60f9033669f024d06ae26a6301260b55 ]
In __blk_mq_tag_busy/idle(), updating 'active_queues' and calculating 'wake_batch' is not atomic:
t1: t2: _blk_mq_tag_busy blk_mq_tag_busy inc active_queues // assume 1->2 inc active_queues // 2 -> 3 blk_mq_update_wake_batch // calculate based on 3 blk_mq_update_wake_batch /* calculate based on 2, while active_queues is actually 3. */
Fix this problem by protecting them wih 'tags->lock', this is not a hot path, so performance should not be concerned. And now that all writers are inside the lock, switch 'actives_queues' from atomic to unsigned int.
Fixes: 180dccb0dba4 ("blk-mq: fix tag_get wait task can't be awakened") Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20230610023043.2559121-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq-debugfs.c | 2 +- block/blk-mq-tag.c | 15 ++++++++++----- block/blk-mq.h | 3 +-- include/linux/blk-mq.h | 3 +-- 4 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index b01818f8e216e..c152276736832 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -427,7 +427,7 @@ static void blk_mq_debugfs_tags_show(struct seq_file *m, seq_printf(m, "nr_tags=%u\n", tags->nr_tags); seq_printf(m, "nr_reserved_tags=%u\n", tags->nr_reserved_tags); seq_printf(m, "active_queues=%d\n", - atomic_read(&tags->active_queues)); + READ_ONCE(tags->active_queues));
seq_puts(m, "\nbitmap_tags:\n"); sbitmap_queue_show(&tags->bitmap_tags, m); diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index a80d7c62bdfe6..100889c276c3f 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -40,6 +40,7 @@ static void blk_mq_update_wake_batch(struct blk_mq_tags *tags, void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx) { unsigned int users; + struct blk_mq_tags *tags = hctx->tags;
/* * calling test_bit() prior to test_and_set_bit() is intentional, @@ -57,9 +58,11 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx) return; }
- users = atomic_inc_return(&hctx->tags->active_queues); - - blk_mq_update_wake_batch(hctx->tags, users); + spin_lock_irq(&tags->lock); + users = tags->active_queues + 1; + WRITE_ONCE(tags->active_queues, users); + blk_mq_update_wake_batch(tags, users); + spin_unlock_irq(&tags->lock); }
/* @@ -92,9 +95,11 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx) return; }
- users = atomic_dec_return(&tags->active_queues); - + spin_lock_irq(&tags->lock); + users = tags->active_queues - 1; + WRITE_ONCE(tags->active_queues, users); blk_mq_update_wake_batch(tags, users); + spin_unlock_irq(&tags->lock);
blk_mq_tag_wakeup_all(tags, false); } diff --git a/block/blk-mq.h b/block/blk-mq.h index a7482d2cc82e7..4542308c8e62f 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -362,8 +362,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx, return true; }
- users = atomic_read(&hctx->tags->active_queues); - + users = READ_ONCE(hctx->tags->active_queues); if (!users) return true;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index de0b0c3e7395a..4110d6e99b2b9 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -748,8 +748,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, struct blk_mq_tags { unsigned int nr_tags; unsigned int nr_reserved_tags; - - atomic_t active_queues; + unsigned int active_queues;
struct sbitmap_queue bitmap_tags; struct sbitmap_queue breserved_tags;